DNA test

Ok so I am pregnant but I'm not sure who the father is. I am still leagally married but my husband and I have been separated and I have been seeing this other guy for the past couple months. The thing is my husband and I also had sex once about a little over a month ago that was a slip up. Both guys know and have agreed to DNA test. My question is have any of u guys ever had to get one done??? And if so how did u do it? I've done some research and am thinking about getting a noninvasive one done but I don't know how accurate those are.